I wear the Galaxy Watch when I sleep to see my sleep score. However, the time I actually fall asleep and the time indicated on the watch are different. For example, it was 1 o'clock when I turned on the sleep mode on the watch and went to sleep, but when I check the time after waking up, it is 12:30.
The sleep mode is more to disable the watch from accidentally waking up.
Eg, with the classics, some people had the function to turn on the watch when you use the ring. By enabling sleep mode, you stop the screen from waking up when the ring is rotated while you sleep.
The auto detect for sleeping looks for movements and if you're not moving too much, it will detect that you're in "sleep mode". Though the algorithm should detect that you're awake during that part of your sleep (the 30 minutes in your case)
